From 7fd7514b10d6580374743071287337d5c7dd9c90 Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee@gmail.com>
Date: Thu, 9 Jul 2026 17:59:32 -0700
Subject: [PATCH 1/2] Add regression test for enum miscompilation

---
 tests/ui/codegen/dont-miscompile-enums.rs | 43 +++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 tests/ui/codegen/dont-miscompile-enums.rs

diff --git a/tests/ui/codegen/dont-miscompile-enums.rs b/tests/ui/codegen/dont-miscompile-enums.rs
new file mode 100644
index 0000000000000..f31a70bf754d6
--- /dev/null
+++ b/tests/ui/codegen/dont-miscompile-enums.rs
@@ -0,0 +1,43 @@
+//@ run-pass
+
+// Bad regression test for https://github.com/rust-lang/rust/issues/159035
+// This should probably be replaced with a codegen test, though that might need to be in LLVM,
+// as it seems that the miscompilation may occur on correct IR misoptimized by SimplifyCFG.
+
+#![allow(dead_code)]
+
+enum Inner {
+    A(u32),
+    B(u32),
+}
+struct Big {
+    _pad: u64,
+    inner: Inner,
+}
+struct Small {
+    a: u16,
+    b: u16,
+    _f: fn(),
+}
+enum Checksum {
+    X(Big),
+    Y(Small),
+}
+impl Checksum {
+    fn finalize(self) -> u32 {
+        match self {
+            Checksum::X(h) => match h.inner {
+                Inner::A(s) => s,
+                Inner::B(s) => s,
+            },
+            Checksum::Y(s) => (u32::from(s.b) << 16) | u32::from(s.a),
+        }
+    }
+}
+#[inline(never)]
+fn run(c: Option<Checksum>) -> Option<u32> {
+    c.map(|c| c.finalize())
+}
+fn main() {
+    println!("{:?}", run(std::hint::black_box(None)));
+}

From 71d2d3d782bb848ad09219ca533370db67249374 Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee@gmail.com>
Date: Thu, 9 Jul 2026 17:55:24 -0700
Subject: [PATCH 2/2] Revert "Only exclude the 155473 change for 1-byte
 bool-likes"

This reverts commit 569ad9986443503f23c534d6c4d9f34e823f5c69.

The PR widened the effect of this from enums with the 0..=1 range to
those with any range if they had more than 1 byte.

Unfortunately, our LLVMIR now incurs miscompilations, so revert until
we find a better fix.
---
 compiler/rustc_abi/src/lib.rs            | 3 +--
 tests/codegen-llvm/function-arguments.rs | 2 +-
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_abi/src/lib.rs b/compiler/rustc_abi/src/lib.rs
index 8e20d3a1dde8b..e26b806dc7397 100644
--- a/compiler/rustc_abi/src/lib.rs
+++ b/compiler/rustc_abi/src/lib.rs
@@ -2103,8 +2103,7 @@ impl Niche {
         let distance_end_zero = max_value - v.end;
         // FIXME: this ought to work for `bool` too, but that seems to be hitting a miscompilation
         // <https://github.com/rust-lang/rust/pull/155473#issuecomment-4302036343>
-        let is_bool = size.bytes() == 1 && v == WrappingRange { start: 0, end: 1 };
-        if count == 1 && !is_bool {
+        if count == 1 && v != (WrappingRange { start: 0, end: 1 }) {
             // We only need one, so just pick the one closest to zero.
             // Not only does that obviously use zero if it's possible, but it also
             // simplifies testing things like `Option<char>`, since looking for `-1`
diff --git a/tests/codegen-llvm/function-arguments.rs b/tests/codegen-llvm/function-arguments.rs
index 924e2fc6c99ec..ef056769b147d 100644
--- a/tests/codegen-llvm/function-arguments.rs
+++ b/tests/codegen-llvm/function-arguments.rs
@@ -265,7 +265,7 @@ pub fn return_slice(x: &[u16]) -> &[u16] {
     x
 }
 
-// CHECK: { i16, i16 } @enum_id_1(i16 noundef{{( range\(i16 -1, 2\))?}} %x.0, i16 %x.1)
+// CHECK: { i16, i16 } @enum_id_1(i16 noundef{{( range\(i16 0, 3\))?}} %x.0, i16 %x.1)
 #[no_mangle]
 pub fn enum_id_1(x: Option<Result<u16, u16>>) -> Option<Result<u16, u16>> {
     x